A known system for treating exhaust gas passing through an exhaust system of a diesel engine comprises a diesel oxidation catalyst (DOC) upstream of a diesel particulate filter (DPF). The combination of these two exhaust gas treatment devices traps diesel particulate matter (DPM) and promotes chemical reactions in exhaust gas as it flows through the exhaust system from the engine, thereby preventing significant amounts of pollutants such as hydrocarbons, carbon monoxide, soot, SOF, and ash, from entering the atmosphere.
Certain sensors are associated with exhaust gas treatment devices like DOC's and DPF's in diesel engine exhaust systems. The sensors provide certain information for control and/or diagnostic purposes. The information may also be used for verifying compliance with relevant regulations. Such verification may require that the functionality of the sensors themselves be verified before further evaluation of the functionality of the exhaust gas treatment system.
Certain government regulations that are anticipated to become applicable to certain motor vehicle engines require certain diagnostic testing of emission control systems. A specific document entitled “Engine Manufacturer Diagnostic System Requirements For 2007 And Subsequent Model-Year Heavy-Duty Engines (EMD)” sets forth certain requirements for assuring functionality of diesel engine exhaust gas treatment systems. Functionality of the sensors associated with the exhaust gas treatment systems needs also to be assured.
Functionality testing of certain sensors is best performed when they are “cold”. To confirm that they are indeed “cold”, it has been proposed to use a timer to time the amount of time that an engine has been shut off since it last was running and to allow further testing only after a certain amount of time has elapsed on the timer.
Such a timer, which is typically implemented in the engine control system, requires power in order to run while the engine is shut off. Some existing engine control systems that are otherwise entirely suitable for use with exhaust gas treatment systems that are subject to the future regulation may not however possess features and the necessary hardware (“keep alive memory” or KAM for example) that allow for measuring engine off time.
Accordingly, a system and method that can verify sensor functionality without having to draw power from a vehicle battery or battery bank for measuring engine off time would be advantageous for those engines.